A printing forme, which, as a rule, is made of copper and which has engraved depressions, is attached to the shell face of a forme cylinder. These engraved depressions are filled with ink by an inking unit. In the course of printing, a paper web is pressed against the forme cylinder by a counter-pressure cylinder and absorbs the ink situated in the depressions. Before the printing forme inked by the inking unit, comes into contact with the paper, excess ink on the printing forme is removed by a doctor blade device, so that ink remains only in the depressions of the printing forme.
An inking unit for a rotogravure rotary printing press is known from EP 0 980 311 B1, and consists substantially of a doctor blade device, an ink trough and a catch basin. The ink trough, as well as the catch basin, of this inking unit can be adjusted in height.
An inking unit for a rotogravure rotary printing press is also known from EP 0 655 328 B1. This unit has an ink trough for receiving ink, an inking roller and a doctor blade device which is acting on the shell face of the forme cylinder. The ink trough of this inking unit is arranged underneath the forme cylinder, and under the inking roller which dips into the ink. A width of the ink trough is furthermore less than a width of the forme cylinder.
Paper webs of greater width are increasingly frequently being processed. Longer forme cylinders, with widths between 1.5 m to 4.5 m, are required for this. In conventional inking units, such wide forme cylinders are inked by the use of appropriately wide inking rollers. However, at such widths, the forme cylinders, as well as the inking rollers, have an increased tendency to sag. In this case, they sag more as their diameter is reduced. In connection with conventional rotogravure rotary printing presses, for use in processing paper webs of great width, it therefore occurs that ink fluctuations up to a complete loss of ink, appear in the finished product. This is because the inking roller rests unevenly against the forme cylinder and the latter is therefore inked, in different degrees, in different areas.
Gaps can even occur between the inking roller and the forme cylinder, so that portions of the printing forme, which is supported by the forme cylinder, are not inked at all. For example, such a gap between the two cylinders occurs in a center area of the cylinder width, if the forme cylinder has a large diameter and the inking roller has a small diameter, so that the inking roller sags more in its center than does the forme cylinder. In connection with a thin forme cylinder, it can happen that the thin forme cylinder sags more than the inking roller. A gap between the forme cylinder and the inking roller is thereby formed in edge areas of the forme cylinder, and the printing forme is not inked there.
DE 42 38 054 C2 discloses an inking unit for a rotogravure forme cylinder. The inking unit includes a single continuous inking roller and an additional shorter support roller.
CH 012 232, U.S. Pat. No. 1,259,394 and DE 17 58 214 U all show inking rollers which are divided in an axial direction of the roller. These divisions are arranged on a common shaft.
In DE 1 230 437 B, there is shown a device in which several inking rollers are placed against a forme cylinder for steel engraving, each of which inking roller transports a separate colored ink. There is no discussion regarding their lengths.